Hydraulic systems include solenoid operated valves that control the flow of pressurized fluid to hydraulically-actuated devices. In these systems, a pilot valve, such as a proportional solenoid valve, controls flow to a large flow control valve for actuation of the control valve. Electronically-controlled solenoid valves tend to provide smoother operation within the hydraulic system when compared to hydro-mechanical shift controls; for example, when used in transmission systems, solenoid valves permit staged or progressive release and application of the clutches (e.g., band clutches or plate clutches) for smoother speed changes.
The electrically-operated valve may be controlled by an electronic controller that controls an operational characteristic, such as line pressure, at the device. For example, the controller may send a signal to the electrically-operated to regulate the supply pressure to the valve, which acts as a primary regulator valve that controls the hydraulically-actuated device. Many applications require the device to change operation frequently, rapidly and precisely (e.g., to handle vehicle speed changes, in the case of a transmission), which in turn requires a high degree of calibration of the electrically-operated controlling the pressure to the device. This level of calibration has been difficult to achieve in practice.
Moreover, control of the electrically-operated, and therefore the device operation, is conducted via an algorithm in the electronic controller using a known calibration curve for the valves. This curve theoretically ensures the desired fluid characteristic response at the hydraulically-actuated device based on the current input to the electrically-operated. In practice, however, maintaining the calibration of the electrically-operated valve to accurately control of the output pressure to the shift actuators is difficult because the output pressure of the valve, which controls the output characteristics of the device, changes as the valve deteriorates or as operating conditions such as temperature, fluid viscosity, and fluid contamination changes. In other words, currently known systems only operate according to a fixed valve calibration and cannot adapt to changing systems or even variations among the valves. Thus, even with tight manufacturing tolerances of the valves and devices, the actual
There is a desire for a system and method that allows closed loop adaptive control of a hydraulic system in real time so that the valve is controlled based on comparing the actual operation of the hydraulically-actuated device with a desired target operation rather than a rigid, predetermined calibration curve of the valve.